The field of the invention is specific applications of photo curable pre-ceramic polymer chemistry to specific applications and more particularly to specific applications such as impregnation and/or coating of ceramic filters for use in combustion engine exhaust systems.
U.S. Pat. No. 3,978,185 teaches melt blown non-woven mats that are prepared from thermoplastic polymer fibers and that are substantially completely free of polymer shot are produced at high polymer throughput rates in a melt blowing process in which thermoplastic polymer resins, preferably polypropylene, having initial intrinsic viscosities of at least 1.4, are degraded, optionally in the presence of a free radical source compound, to have both reduced intrinsic viscosities and an apparent viscosity in the melt-blowing nozzle orifices of from about 50 to about 300 poise.
U.S. Pat. No. 5,322,537 teaches an exhaust gas filter for internal combustion engines and having a honeycomb structure that includes a ceramic fiber and an inorganic binder. The ceramic fiber consists essentially of Al.sub.2 O.sub.3 and SiO.sub.2. The inorganic binder includes Al.sub.2 O.sub.3 and SiO.sub.2 to bind the ceramic fiber. The inorganic binder is of a single glass phase or of a mixed phase of a glass phase and a crystal phase both having the same crystal structure in the temperature range of 20.degrees to 1200.degrees C. In the inorganic binder, a crystal such as quartz which produces abnormal expansion due to crystal phase transition is excluded, and occurrence of cracking is prevented.
In recent years, air pollution by NOx or floating small particulates has developed in large cities. As for the small particulates floating in the air, 20 to 30% of them are said to be produced by black smoke exhausted by Diesel engines of automobiles. As a counter-measure against the black smoke, there is provided an exhaust gas cleaner which, placed in the exhausting system, comprises a filter to trap small particulates in the exhaust gas and a refreshing apparatus to burn the trapped particulates. Among the conventional filters, a ceramic monolithic type is known as is disclosed in U.S. Pat. No. 4,364,761 incorporated herein by reference. This conventional ceramic monolithic filter comprises many long cells arranged side-by-side to form a honeycomb structure, one cell having an inlet at one end thereof and being plugged at the other end, and an adjacent cell being plugged at the same end as the inlet of the first cell but having an outlet at the other end. When the exhaust gas enters the inlet and passes along the porous wall between the cells, the particulate in the gas is trapped. If an amount of trapped particulate increases, the porous walls are choked, of course, by the particulates. This results in an increase of back pressure of the engine. It is necessary, when the trapped particulates exceeded a certain amount, to remove the particulates to suppress the load increase on the engine due to increased back pressure. The particulates consist of solid carbon and soluble organic fraction (SOF) which is soluble in an organic solvent such as dichloromethane, both being combustible and burned if heated over 600.degrees C., although the temperature somewhat varies depending upon the kind or loading condition of the engine. Thus, the exhaust gas cleaner is provided with a filter regenerating apparatus such as an electric heater or gas burner. For the exhaust gas filter, it is necessary that it not be choked or molten when heated for regenerating, and, usually is a porous material of large porosity and high melting temperature.
U.S. Pat. No. 4,652,286 teaches an exhaust gas filter for diesel particulates that includes a row of a plurality of channels of honeycomb structure of porous sintered ceramic fiber composite sheet, the ceramic fiber composite sheet which slurry of alumino-silicate fiber and fire clay produces by a paper-forming method. The honeycomb structure of the ceramic fiber composite sheet is formed by stacking plane sheets and corrugated sheets one atop the other. The filter exhibits low pressure drop yet highly efficient operation by having a bulk density of the ceramic fiber composite sheet in the range of 0.1 g/cm.sup.3 to 0.8 g/cm.sup.3. Particulates such as soot contained in the exhaust gas of diesel engines have recently been reported to be carcinogenic and it is therefore desirable to eliminate such particles from exhaust gases. Although combustors and engines are being improved in order to reduce the emission of such particulates, for the present time it is considered best to trap the particulates with a filter and then burn the particulates trapped on the filter. Various methods have been proposed for eliminating the particulates in exhaust gases. Conventional proposals include metal mesh or ceramic fibers packed and sealed in a container as a filter element. Porous ceramic foams or extruded ceramic honeycombs are also used. Devices using a metal mesh or packed ceramic fiber randomly filled as the filler element are apt to blow off the fibers, particularly ceramic fibers, during operation resulting in poor filtration. The metal mesh may encounter a problem of melting down during regenerating the filtering function in which the trapped particulates are burnt. The ceramic foam and the extruded ceramic honeycomb often have insufficient thermal shock resistance. The extruded ceramic honeycomb has an insufficient gas permeability which causes a large pressure drop, because it cannot be structured to have a large porosity.
U.S. Pat. No. 6,444,006 teaches a high temperature composite ceramic filter that has a particular use as a diesel engine exhaust filter. Aqueous slurry containing short ceramic fibers, organic fibers and a water soluble thermoplastic binder is formed into a sheet and dried. The dried sheet is then fabricated into a three-dimensional green filter structure and a binder, either a liquid solution of a thermosetting resin or a colloidal solution of a ceramic material, is applied to the filter structure to increase the temperature stability of the green structure. The filter structure is then fired at an elevated temperature sufficient to remove the organic constituents and is subsequently coated with silicon carbide by a chemical vapor deposition process to provide a composite ceramic filter having high temperature resistance, durability and improved performance.
As regulatory agencies have recently mandated the reduction of particulate emissions in diesel engines, there has been increased activity in the development of exhaust gas filters for diesel engines. A typical exhaust filter will trap the particulate material contained in the exhaust stream, and to prevent clogging of the filter and the resultant increase of load on the engine due to increased back pressure, the particulate material is then burned from the filter. As a diesel engine exhaust filter must have high temperature resistance and durability, it has been proposed to utilize ceramic materials as the filter media. For example, a ceramic filter for use in gas turbine engines which U.S. Pat. No. 4,017,347 describes. A ceramic tape or sheet is prepared from the slurry containing ceramic particles and a two-resin binder system composed of a thermoplastic resin and a thermosetting resin. The tape is formed into a filter structure and the structure is then fired to sinter the ceramic particles and bum out the organic constituents, thus producing a sintered ceramic cellular structure.
Extruded ceramic monolith diesel particulate filters have limited temperature resistance and have higher back pressure than fiber filters. Fiber filters made from a ceramic based paper perform better (i.e. lower back pressure), but require a binder phase which can be difficult to apply and expensive. Using a melt-blown pre-ceramic fiber allows manipulation and bonding of the ceramic form while in a more malleable pre-ceramic thermoplastic polymer form. As a thermoplastic, heat can be used to bond the fibers together and to aid in shaping the media into a filter. The media can be formed using a process similar to ones currently employed in the prior art with conventional thermoplastic polymers. The polymer can be cured (cross-linked) into a thermo-set polymer before thermal decomposition from polymer to ceramic. Possible curing processes include steam curing of silane groups and UV or visible light curing of allyl groups, among others. Additives (as a component in a mixture, as a copolymer, or as a functional group on the polymer) might be used to enable or enhance curing below the melting point. Additionally the pre-ceramic polymer may be used for any bonding, sealing or reinforcement when producing a fabricated part. Conversion to a thermo-set will reduce or eliminate deformation during decomposition to a ceramic (e.g. slumping, melting and sintering). The resulting filters will be homogenous in composition not needing binders added, and the temperature limit can be 1500.degrees C. or higher, depending on the composition of the ceramic material produced.
U.S. Pat. No. 4,806,612 teaches pre-ceramic actylenic polysilanes which contain —(CH(2))(w) C.tbd.CR′ groups attached to silicon where w is an integer from 0 to 3 and where R′ is hydrogen, an alkyl radical containing 1 to 6 carbon atoms, a phenyl radical, or an —SiR″′(3) radical wherein R″′ is an alkyl radical containing 1 to 4 carbon atoms. The acetylenic polysilanes are prepared by reacting chlorine- or bromine-containing polysilanes with either a Grignard reagent of general formula R′C.tbd.C(CH(2))(w) MgX′ where w is an integer from 0 to 3 and X′ is chlorine, bromine, or iodine or an organo-lithium compound of general formula R′C.tbd.C(CH(2))(w) Li where w is an integer from 0 to 3. The acetylenic polysilanes can be converted to ceramic materials by pyrolysis at elevated temperatures under an inert atmosphere.
U.S. Pat. No. 4,800,211 teaches 3-Hydroxybenzo[b]thiophene-2-carboxamide derivatives which have been prepared by: (1) treating a substituted 2-halobenzoate with a thioacetamide; (2) treating a substituted thiosalicylate with an appropriately substituted haloacetamide; and (3) further synthetic modification of compounds prepared above. These compounds have been found to be effective inhibitors of both cyclooxygenase and lipoxygenase and thereby useful in the treatment of pain, fever, inflammation, arthritic conditions, asthma, allergic disorders, skin diseases, cardiovascular disorders, psoriasis, inflammatory bowel disease, glaucoma or other prostaglandins and/or leukotriene mediated diseases.
U.S. Pat. No. 4,588,832 teaches a novel and economical route for the synthetic preparation of a 1-alkynyl trihydrocarbyl silane compound. The method includes the steps of reacting metallic sodium with a hydrocarbyl-substituted acetylene or allene compound to form a substituted sodium acetylide and re-acting the acetylide with a trihydrocarbyl monohalogenosilane in the reaction mixture which is admixed with a polar organic solvent such as dimethylformamide.
U.S. Pat. No. 4,505,726 teaches an exhaust gas cleaning device provided with a filter member that collects carbon particulates in exhaust gases discharged from a diesel engine and an electric heater for burning off the particulates collected by the filter member. The filter member is composed of a large number of intersecting porous walls which define a large number of inlet gas passages and outlet gas passages which are adjacent to each other. The electric heater is composed of at least one film-shaped heating resistor which is directly formed on the upstream end surface of the filter member so as to be integral therewith. When the amount of carbon particulates collected by the filter member reaches a predetermined level, electric current is supplied to the electric heater. The carbon particulates adhered to the upstream end surface of the filter member are ignited and burnt off. Then, the combustion of carbon particulates spreads to the other carbon particulates collected in the other portion of the filter member.
U.S. Pat. No. 5,843,304 teaches a materials treatment system which includes filtration and treatment of solid and liquid components of a material, such as a waste material. A filter or substrate assembly is provided which allows liquids to pass there-through, while retaining solids. The solids are then incinerated utilizing microwave energy, and the liquids can be treated after passing through the filter element, for example, utilizing a treatment liquid such as an oxidant liquid. The filter assembly can also include an exhaust filter assembly which removes solids or particulate matter from exhaust gasses, with the retained solids/particulates incinerated utilizing microwave energy.
U.S. Pat. No. 5,074,112 teaches a filter assembly for an internal combustion engine which includes, in combination, a housing defining an exhaust gas passage having an inlet end and an outlet end and a cavity intermediate the inlet and outlet ends thereof and in serial fluid communication therewith, the cavity defining an electromagnetically resonant coaxial line waveguide, a filter disposed within the cavity for removing particulate products of combustion from exhaust gases passing through the cavity, and a mechanism for producing axisymmetrically distributed, standing electromagnetic waves within the cavity whereby to couple electromagnetic energy in the waves into lossy material in the cavity to produce heat for incinerating the particulate products of combustion accumulated on the filter.
U.S. Pat. No. 4,934,141 teaches a device for microwave elimination of particles contained in the exhaust gases of diesel engines in which a microwave source and a conductor of the electromagnetic field generated by the source is joined with a resonator mounted on an element of the pipe for the exhaust gases which contains an insert, characterized by the fact that the insert consists of a filter whose upstream and downstream ends are offset toward the inside of the cavity defined by the resonator and delimit two chambers in which conductors of the electro-magnetic field come out, respectively.
U.S. Pat. No. 4,825,651 teaches a device and method for separating soot or other impurities from the exhaust gases of an internal-combustion engine, particularly a diesel internal-combustion engine, comprises a microwave source that is coupled to the intermediate section of the exhaust pipe that is constructed for the development of an electromagnetic field, an effective burning of the soot with a low flow resistance, the intermediate section being developed as a cavity resonator and at its exhaust gas inlet and exhaust gas outlet, is equipped with a metal grid, and an insert made of a dielectric material in the cavity resonator concentrates the exhaust gas flow in the area of high energy density of the electromagnetic field.
U.S. Pat. No. 4,477,771 teaches conductive particulates in the form of soot which are collected from diesel engine exhaust gases on a porous wall monolithic ceramic filter in such a way that the soot is somewhat uniformly distributed throughout the filter. The filter is housed in a chamber having a property of a microwave resonant cavity and the cavity is excited with microwave energy. As the particulates are collected the cavity appears to the microwaves to have an increasing dielectric constant even though the matter being accumulated is conductive rather than dielectric so that as collected on the porous filter it has the property of an artificial dielectric. The response of the cavity to the microwave energy is monitored to sense the effect of the dielectric constant of the material within the cavity to provide a measure of the soot content in the filter.
U.S. Pat. No. 5,902,514 teaches a material for microwave band devices which are used by the general people and in industrial electronic apparatuses. Particularly, a magnetic ceramic composition for use in microwave devices, a magnetic ceramics for use in microwave devices and a preparation method therefore are disclosed, in which the saturation magnetization can be easily controlled, and a low ferri-magnetic resonance half line width and an acceptable curie temperature are ensured. The magnetic ceramic composition for microwave devices includes yttrium oxide Y(2)O(3)), iron oxide (Fe(2)O(3)), tin oxide (SnO(2)), aluminum oxide (Al(2)O(3)) and a calcium supply source. The magnetic ceramics for the microwave devices are manufactured by carrying out a forming and a sintering after mixing: yttrium oxide, iron oxide, tin oxide, aluminum oxide and calcium carbonate (or calcium oxide) based on a formula shown below. It has a saturation magnetization of 100-1,800 G at the normal temperature, a temperature coefficient for the saturation magnetization of 0.2%/degrees C., and a ferri-magnetic resonance half line width of less than 60 Oe, Y(3−x)Ca(x/2)Sn(x/2)Fe(5−y)Al(y)O(12) where 0.1<=x<=1, and 0.1<=y<=1.5.
U.S. Pat. No. 5,843,860 teaches a ceramic composition for high-frequency dielectrics which includes the main ingredients of ZrO(2), SnO(2) and TiO(2) and a subsidiary ingredient of (Mn(NO(3))(2).4H(2)O). A homogeneous ceramic composition can be prepared by a process which comprises the steps of: adding ZrO(2), SnO(2) and TiO(2) by the molar ratio to satisfy (ZrO(2))(1−x) (SnO(2))(x)(TiO(2))(1+y) (wherein, 0.1M degrees C. or above; and, adding 1% or less of Mn(NO(3))(2).4H(2)O by weight of MnO to a mixture. The ceramic composition of the invention has a high dielectric constant of 40 or more, a quality factor of 7000 or more, and a temperature coefficient of resonance frequency below 10. Accordingly, it can be used for an integrated circuit at microwave as well as at high frequency, or for dielectric resonators.
U.S. Pat. No. 5,808,282 teaches a microwave susceptor bed which is useful for sintering ceramics, ceramic composites and metal powders. The microwave susceptor bed contains granules of a major amount of a microwave susceptor material, and a minor amount of a refractory parting agent, either dispersed in the susceptor material, or as a coating on the susceptor material. Alumina is the preferred susceptor material. Carbon is the most preferred parting agent. A sintering process uses the bed to produce novel silicon nitride products.
U.S. Pat. No. 5,446,270 teaches a composition which includes susceptors having the capability of absorbing microwave energy and a matrix. The susceptors includes a particulate substrate substantially non-reflective of microwave energy and a coating capable of absorbing microwave energy. The matrix is substantially non-reflective of microwave energy. Susceptors are typically particles having a thin-film coating thereon. The matrix typically includes polymeric or ceramic materials that are stable at temperatures conventionally used in microwave cooking. The composition allows reuse of the susceptors, eliminates decline in heating rate, eliminates arcing, allows the heating rate to be controlled, allows overheating to be controlled, and allows formation of microwave heatable composite materials having very low metal content.
U.S. Pat. No. 5,365,042 teaches a heat treatment installation for parts made of a composite material which has a ceramic matrix and which includes a treatment enclosure. The treatment enclosure is connected to a microwave generator by a wave-guide and which includes a press for hot pressing a part to be treated in the enclosure and a gas source for introducing a protective gas into the enclosure.
U.S. Pat. No. 5,126,529 teaches a method for forming a three-dimensional object by thermal spraying which utilizes a plurality of masks positioned and removed over a work surface in accordance with a predetermined sequence. The masks correspond to cross sections normal to a centerline through the work-piece. One set of masks defines all cross sections through the work-piece. A second set of masks contains at least one mask. The mask corresponds to each mask of the first set. Masks from each set are alternatively placed above a work surface and sprayed with either a deposition material from which the work-piece will be made or a complementary material. In this manner, layers of material form a block of deposition material and complementary material. The complementary material serves as a support structure during forming and is removed. Preferably, the complementary material has a lower melting temperature than the deposition material and is removed by heating the block. Alternatively, one could mask only for the deposition material and remove complementary material overlying the deposition material after each spraying of complementary material.
U.S. Pat. No. 4,199,387 teaches an air filter unit of the pleated media, high efficiency type. The media pleat edges are sealed to the supporting frame to prevent bypass of air with a ceramic adhesive and fibrous ceramic mat which allows the unit to be exposed to high temperatures (e.g., up to 2000 degrees F.) without danger of seal breakdown. While in the form of slurry the adhesive is applied, for example, with a trowel to the zig-zag pleated edges of the media that, together with corrugated spacers, forms the filter core. The latter is then surrounded on four sides by the compressible mat of fibrous ceramic material and inserted in a box-like support frame with the slurry filling the space between the pleated edges of the media and the fibrous mat. The filter core and surrounding mat are assembled with the support frame while the slurry is still wet whereby upon hardening the resulting layers of ceramic cement provide a complete, heat-resistant seal while avoiding cracking in normal handling due to the resilience of the compressed fibrous mat which maintains an airtight seal between hardened ceramic and support frame.
U.S. Pat. No. 6,063,150 teaches a self-cleaning particle filter for Diesel engines which includes filter housing, control circuitry, a removable filter sandwich and independent power source. The removable filter sandwich includes a number of sintered metal strips sewn and positioned between two sheets of inorganic material to provide a filter sandwich. Current is delivered to the metal filter strips to efficiently burn off carbon, lube oil and unburned fuel particulates which have been filtered from exhaust gas. The filter sandwich is formed into a cylindrical configuration and mounted onto a perforated metal carrier tube for receiving and filtering exhaust gas.
U.S. Pat. No. 6,101,793 teaches an exhaust gas filter having a ceramic filter body is configured such that a specific heat h (cal/g degrees C.) of ceramic powder constituting the body, and a bulk specific gravity d (g/cm(^3)) of the filter, satisfy the relation 0.12 (cal/cm(^3) degrees C.)<=h*d<=0.19 (cal/cm(^3) degrees C.). The ceramic filter body includes a plurality of cells which extend axially to open at opposite ends of the body. One of the opposite axial ends of each of the cells is closed by filler in such a manner that the closed ends of the cells and the open ends of the cells are arranged in an alternating configuration. The filter traps particulates in the exhaust gas, and the trapped particulates are removed by regeneration combustion of the filter. The filter exhibits excellent durability, thus preventing the formation of cracks in the surface and interior of the filter. When the filter is mounted on a diesel engine, the diesel engine advantageously does not discharge black smoke.
U.S. Pat. No. 5,756,412 teaches a dielectric ceramic composition for microwave applications which consists essentially of the compound having a formula B′B(2)″O(6), wherein B′ is at least one metal selected from the group of Mg, Ca, Co, Mn, Ni and Zn, and wherein B″ is one of Nb or Ta, and additionally includes at least one compound selected from the group of CuO, V(2)O(5), La(2)O(3), Sb(2)O(5), WO(3), MnCO(3), MgO, SrCO(3), ZNO, and Bi(2)O(3) as an additive, wherein the amount of the additive is 0.05% to 2.0% by weight of the total weight of the composition.
The synthesis of polycarbosilane from the pyrolytic condensation reaction of polydimethylsilane obtained from the reaction of dichlorodimethylsilane with an alkali metal, such as sodium. In the latter approach, polydimethylsilane can be prepared by Würtz type coupling of dichlorodimethylsilane with sodium in toluene. The direct pyrolysis of polydimethylsilane, a viscous thermoplastic resin, at high temperature gives SiC in a ceramic yield of about 30%-40%. By thermally cross-linking the polydimethylsilane into an infusible rigid thermoset polymer, which is insoluble in any common solvents, the subsequent pyrolysis yield is on the order of 88%-93%. This thermolysis was accomplished by refluxing the polydimethyl-silane to in excess of 350° C.
Numerous pre-ceramic polymers with improved yields of the ceramic have been described in U.S. Pat. No. 5,138,080, U.S. Pat. No. 5,091,271, U.S. Pat. No. 5,051,215 and U.S. Pat. No. 5,707,471. Fundamental chemistry contained is specific to the process employed and mainly leaves the pre-ceramic polymer in a thermoplastic state. These pre-ceramic polymers which catalytic or photo-induced cross-linking do not satisfy the high ceramic yield, purity and fluidity in combination with low temperature cross-linking ability necessary for producing large densified ceramic structures in a single step continuous process.
U.S. Pat. No. 5,138,080 teaches novel polysilamethylenosilane polymers which have polysilane-polycarbo-silane skeleton which can be prepared in one-step reaction from mixtures of chlorosilaalkanes and organochloro silanes with alkali metals in one of appropriate solvents or in combination of solvents thereof. Such polysilamethylenosilane polymers are soluble and thermoplastic and can be pyrolyzed to obtain improved yields of silicon carbide at atmospheric pressure.
U.S. Pat. No. 5,091,271 teaches a shaped silicon carbide-based ceramic article which has a mechanical strength which is produced at a high efficiency by a process including the step of forming an organic silicone polymer, for example, polycarbosilastyrene copolymer, into a predetermined shape, for example, a filament or film; doping the shaped polymer with a doping material consisting of at least one type of halogen, for example, bromine or iodine, in an amount of 0.01% to 150% based on the weight of the shaped polymer, to render the shaped polymer infusible; and pyrolyzing the infusible shaped polymer into a shaped SiC-based ceramic article at a temperature of 800° C. to 1400° C. in an inert gas atmosphere, optionally the halogen-doped shaped polymer being treated with a basic material, for example, ammonia, before the pyrolyzing step, to make the filament uniformly infusible.
U.S. Pat. No. 5,300,605 teaches poly(I-hydro-l-R-1-silapent-3-ene) homo-polymers and copolymers which contain silane segments with reactive silicon-hydride bonds and contain hydrocarbon segments with cis and trans carbon-carbon double bonds.
U.S. Pat. No. 5,171,810 teaches random or block copolymers with (I-hydro-I—R—I-sila-cis-pent-3-ene), poly(I-hydro-1-R-3,4 benzo-l-sila pent-3-ene) and disubstituted I-silapent-3-ene repeating units of the general formula ##STRI## where R is hydrogen, an alkyl radical containing from one to four carbon atoms or phenyl, R.sup.1 is hydrogen, an alkyl radical containing from one to four carbon atoms, phenyl or a halogen and R.sup.2 is hydrogen, or R.sup.1 and R.sup.2 are combined to form a phenyl ring, are prepared by the anionic ring opening polymerization of silacyclopent-3-enes or 2-silaindans with an organometallic base and cation coordinating ligand catalyst system or a metathesis ring opening catalyst system.
U.S. Pat. No. 5,169,916 Poly(I-hydro-I—R—I-sila-cis-pent-3-ene) and poly(I-hydro-I—R-3,4 benzo-l-sila pent-3-ene) polymers which has repeating units of the general formula polycarbosilane containing at least two tbd.SiH groups per molecule via intimately contacting such fusible polycarbosilane with an effective hardening amount of the vapors of sulfur.
U.S. Pat. No. 5,064,915 teaches insoluble polycarbosilanes, readily pyrolyzed into silicon carbide ceramic materials such as SiC fibers, are produced by hardening a fusible polycarbosilane containing at least two tbd.SiH groups per molecule via intimately contacting such fusible polycarbosilane with an effective hardening amount of the vapors of sulfur.
U.S. Pat. No. 5,049,529 teaches carbon nitride ceramic materials which are produced by hardening a fusible polycarbosilane containing at least two tbd.SiH groups per molecule by intimately contacting such fusible polycarbosilane with an effective hardening amount of the vapors of sulfur, next, heat treating the infusible polycarbosilane which results under an ammonia atmosphere to such extent as to introduce nitrogen into the infusible polycarbosilane without completely removing the carbon therefrom and then heat treating the nitrogenated polycarbosilane in a vacuum or in an inert atmosphere to such extent as to essentially completely convert it into a ceramic silicon carbon nitride.
U.S. Pat. No. 5,051,215 teaches a rapid method of infusibilizing pre-ceramic polymers which includes treatment of the polymers with gaseous nitrogen dioxide. The infusibilized polymers may be pyrolyzed to temperatures in excess of about 800° C. to yield ceramic materials with low oxygen content and, thus, good thermal stability. The methods are especially useful for the production of ceramic fibers and, more specifically, to the on-line production of ceramic fibers.
U.S. Pat. No. 5,028,571 teaches silicon nitride ceramic materials which are produced by hardening a fusible polycarbosilane containing at least two dbd.SiH groups per molecule by intimately contacting such fusible polycarbosilane with an effective hardening amount of the vapors of sulfur and then pyrolyzing the infusible polycarbosilane which results under an ammonia atmosphere.
U.S. Pat. No. 4,847,027 teaches a method for the preparation of ceramic materials or articles by the pyrolysis of pre-ceramic polymers wherein the pre-ceramic polymers are rendered infusible prior to pyrolysis by exposure to gaseous nitric oxide. Ceramic materials with low oxygen content, excellent physical properties, and good thermal stability can be obtained by the practice of this process. This method is especially suited for the preparation of ceramic fibers.
U.S. Pat. No. 5,714,025 teaches a method for preparing a ceramic-forming pre-preg tape which includes the steps of dispersing in water a ceramic-forming powder and a fiber, flocculating the dispersion by adding a cationic wet strength resin and an anionic polymer, dewatering the flocculated dispersion to form a sheet, wet pressing and drying the sheet, and coating or impregnating the sheet with an adhesive selected from the group consisting of a polymeric ceramic precursor, and a dispersion of an organic binder and the materials used to form the sheet. The tape can be used to form laminates, which are fired to consolidate the tapes to a ceramic.
U.S. Pat. No. 5,707,471 teaches a method for preparing fiber reinforced ceramic matrix composites which includes the steps of coating refractory fibers, forming the coated fibers into the desired curing the coated fibers to form a pre-preg, heating the pre-preg to form a composite and heating the composite in an oxidizing shape, environment to form an in situ sealant oxide coating on the composite. The refractory fibers have an interfacial coating thereon with a curable pre-ceramic polymer which has a char containing greater than about 50% sealant oxide atoms. The resultant composites have good oxidation resistance at high temperature as well as good strength and toughness.
U.S. Pat. No. 5,512,351 teaches a new pre-preg material which has good tack drape properties and feasible out-time. The pre-preg material is prepared by impregnating inorganic fibers with a composition which includes a fine powder of a metal oxide or oxides having an average particle diameter of not larger than one micrometer, a soluble siloxane polymer having double chain structure, a tri-functional silane compound having at least one ethylenically unsaturated double bond in the molecule thereof, a organic peroxide and a radically polymerizable monomer having at least two ethylenically unsaturated double bonds and heating the impregnated fibers.
U.S. Pat. No. 4,835,238 teaches a reaction of 1,1-dichloro-silacyclobutanes with nitrogen-containing di-functional nucleophiles which gives polysilacyclobuta-silazanes which can be cross-linked and also converted to ceramic materials.
Numerous processing mechanics with various direct applications have been described, for example, in the U.S. Pat. No. 5,820,483, U.S. Pat. No. 5,626,707, U.S. Pat. No. 5,732,743 and U.S. Pat. No. 5,698,055. Process mechanics are for a single product process and do not permit continuous curing and pyrolysis in a single step to produce highly dense thick ceramic components.
U.S. Pat. No. 5,820,483 teaches methods for manufacturing a shaft for a golf club. A plug is detachably affixed to a distal end of a mandrel. A plurality of plies of pre-preg composite sheet are wrapped around the mandrel and plug and, thereafter, heated causing the resin comprising the various plies to be cured. The mandrel is then removed from the formed shaft, leaving the plug as an integral part of the distal tip of the shaft.
U.S. Pat. No. 5,626,707 teaches an apparatus which produces a composite tubular article. The apparatus includes a frame, a drive mechanism for rotating a mandrel, at least two spindles mounted to the frame, a tensioner and a belt extending between the first and second spindles. The apparatus may be used to roll pre-preg strips or similar sheets of composite materials around the mandrel. The belt travels over the spindles, and the spindles guide the belt through changes in its direction of travel. The mandrel is mounted in the drive mechanism in contact with the belt, which changes its direction of travel around the mandrel. The lower surface of the belt bears against upper portions of the spindles, and the mandrel contacts the upper surface of the belt. As the drive mechanism rotates the mandrel, pre-preg sheets are fed between the mandrel and the belt and are thereby wrapped around the mandrel. The belt presses the pre-preg sheets against the mandrel. The wrapped mandrel may then be removed from the apparatus and cured in any suitable manner known in the art to produce a composite tubular article.
U.S. Pat. No. 5,732,743 teaches a method for joining and repairing pipes includes the step of utilizing photo-curable resins in the form of a fabric patch to for quickly repairing or sealing pipes. A photo-curable flexible pre-preg fabric is wrapped over the entire area of the pipe to be joined or repaired. The pre-preg fabric contains multiple layers of varying widths and lengths. The pre-preg fabric is then exposed to photo-radiation which cures and seals the pipe.
U.S. Pat. No. 5,698,055 teaches a method for making a reinforced tubular laminate. A dry braided fiber sleeve is placed between a mandrel and spiral tape wrap either over, under, or layered with a pre-preg material. During the initial stages of the curing process, while the temperature is rising, the resin in the pre-preg material flows and wets out the dry braid. When the final cure takes place, the braid becomes an integral part of the finished laminate. The choice of fiber materials and braid angle permits various tubular laminate strengths. The selection of fiber colors and patterns permit a wide variety of tubular laminate aesthetic characteristics.
U.S. Pat. No. 5,632,834 teaches sandwich structures which are made of fiber-reinforced ceramics. The base substance of the ceramic matrix consists of a Si-organic polymer and a ceramic or metallic powder. A cross-linking of the Si-organic polymer takes place under increased pressure and at an increased temperature. After the joining of the facings and the honeycomb core, the sandwich structure is pyrolysed to form a ceramic material
U.S. Pat. No. 5,641,817 teaches organo-metallic ceramic precursor binders which are used to fabricate shaped bodies by different techniques. Exemplary shape making techniques which utilize hardenable, liquid, organo-metallic, ceramic precursor binders include the fabrication of negatives of parts to be made, such as sand molds and sand cores for metal-casting, as well as utilizing ceramic precursor binders to make shapes directly, such as brake shoes, brake pads, clutch parts, grinding wheels, polymer concrete, refractory patches and liners. A thermo-settable, liquid ceramic precursor provides suitable-strength sand molds and sand cores at very low binder levels and, upon exposure to molten metal casting exhibit low emissions toxicity as a result of their high char yields of ceramic upon exposure to heat. The process involves the fabrication of pre-forms used in the formation of composite articles. Production costs and relatively poor physical properties prohibit their inherently large cost of capitalization, high wide use.
U.S. Pat. No. 4,631,179 teaches this ring-opening-polymerization reactions method to obtain a linear polymer of the formula [SiH.sub.2 CH.sub.2].sub.n. This polymer exhibit ceramics yields up to 85% on pyrolysis. The starting material for the ring-opening-polymerization reaction was the cyclic compound [SiH.sub.2 CH.sub.2].sub.2, which is difficult and costly to obtain in pure form by either of the procedures that have been reported.
U.S. Pat. No. 5,888,641 teaches an exhaust manifold for an engine which is made of all fiber reinforced ceramic matrix composite material so as to be light weight and high temperature resistant. A method of making the exhaust manifold includes the steps of forming a liner of a cast monolithic ceramic material containing pores, filling the pores of the cast monolithic ceramic material with a pre-ceramic polymer resin, coating reinforcing fibers with an interface material to prevent a pre-ceramic polymer resin from adhering strongly to the reinforcing fibers, forming a mixture of a pre-ceramic polymer resin and reinforcing fibers coated with the interface material, forming an exhaust manifold shaped structure from the mixture of the pre-ceramic polymer resin and the reinforcing fibers coated with the interface material by placing the mixture on at least a portion of the cast monolithic ceramic material, and firing the exhaust component shaped structure at a temperature and a time sufficient to convert the pre-ceramic polymer resin to a ceramic thereby forming a reinforced ceramic composite.
U.S. Pat. No. 5,153,295 teaches compositions of matter which have potential utility as precursors to silicon carbide. These compositions are obtained by a Grignard coupling process starting from chlorocarbosilanes, a readily available class of compounds. The new precursors constitute a fundamentally new type of polycarbosilane that is characterized by a branched, [Si—C].sub.n “backbone” which consists of SiR.sub.3 CH.sub.2-, —SiR.sub.2 CH.sub.2-, .dbd.SiRCH.sub.2-, and .tbd.SiCH.sub.2- units (where R is usually H but can also be other organic or inorganic groups, e.g., lower alkyl or alkenyl, as may be needed to promote cross-linking or to modify the physical properties of the polymer or the composition of the final ceramic product). A key feature of these polymers is that substantially all of the linkages between the Si—C units are “head-to-tail”, i.e., they are Si to C. The polycarbosilane “SiH.sub.2 CH.sub.2” has a carbon to silicon ratio of 1 to 1 and where substantially all of the substituents on the polymer backbone are hydrogen. This polymer consists largely of a combination of the four polymer “units”: SiH.sub.3 CH.sub.2-, —SiH.sub.2 CH.sub.2-, .dbd.SiHCH.sub.2-, and -.tbd.SiCH.sub.2- which are connected “head-to-tail” in such a manner that a complex, branched structure results. The branched sites introduced by the last two “units” are offset by a corresponding number of SiH.sub.3 CH.sub.2- “end groups” while maintaining the alternating Si—C “backbone”. The relative numbers of the polymer “units” are such that the “average” formula is SiH.sub.2 CH.sub.2. These polymers have the advantage that it is only necessary to lose hydrogen during pyrolysis, thus ceramic yields of over 90% are possible, in principle. The extensive Si—H functionality allows facile cross-linking and the 1 to 1 carbon to silicon ratio and avoids the incorporation of excess carbon in the SiC products that are ultimately formed. The synthetic procedure employed to make them allows facile modification of the polymer, such as by introduction of small amounts of pendant vinyl groups, prior to reduction. The resulting vinyl-substituted “SiH.sub.2 CH.sub.2” polymer has been found to have improved cross-linking properties and higher ceramic yield.
A pre-ceramic polymer is prepared by a thermally induced methylene insertion reaction of polydimethylsilane. The resulting polymer is only approximately represented by the formula [SiHMeCH.sub.2].sub.n, as significant amounts of un-reacted (SiMe.sub.2).sub.n units, complex rearrangements, and branching are observed. Neither the preparation nor the resulting structure of this precursor is therefore similar to the instant process. In addition to the carbosilane “units”, large amounts of Si—Si bonding remains in the “backbone” of the polymer. This polymer, in contrast to the instant process, contains twice the stoichio-metric amount of carbon for SiC formation. The excess carbon must be eliminated through pyrolytic processes that are by no means quantitative. Despite the shortcomings, this polymer has been employed to prepare “SiC” fiber. However, it must be treated with various cross-linking agents prior to pyrolysis which introduce contaminants. This results in a final ceramic product that contains significant amounts of excess carbon and silica which greatly degrade the high temperature performance of the fiber.
SiC precursors predominately linear polycarbo-silanes have been prepared via potassium de-chlorination of chloro-chloromethyl-dimethylsilane. The resulting polymers have not been fully characterized, but probably contain significant numbers of Si—Si and CH.sub.2-CH.sub.2 groups in the polymer backbone. The alkali metal dechlorination process used in the synthesis of such materials does not exhibit the selective head-tail coupling found with Grignard coupling. The pendant methyl groups in such materials also lead to the incorporation of excess carbon into the system. In several polymer systems mixtures containing vinylchlorosilanes (such as CH.sub.2.dbd.CH—Si(Me)Cl.sub.2) and Me.sub.2 SiCl.sub.2 are coupled by de-chlorination with potassium in tetrahydro-furan. U.S. Pat. No. 4,414,403 and U.S. Pat. No. 4,472,591 both teach this method. The “backbone” of the resulting polymers consists of a combination of Si—Si and Si—CH.sub.2 CH(—Si).sub.2 units. Later versions of this polymer Me(H)SiCl.sub.2 in addition to the Me.sub.2 SiCl.sub.2 and are subjected to a sodium-hydrocarbon de-chlorination process which does not attack vinyl groups. The resulting polymer consists of a predominately linear, Si—Si “backbone” bearing pendant methyl groups, with some Si—H and Si—CH.dbd.CH.sub.2 functionality to allow cross-linking on pyrolysis.
None of these precursors derived using vinylchlorosilanes are similar to those of the process in that having predominantly Si—Si bonded “backbones”, they are essentially polysilanes, not polycarbosilanes. In addition, the carbon in these polymers is primarily in the form of pendant methyl functionality and is present in considerable excess of the desirable 1 to 1 ratio with silicon. The ceramic products obtained from these polymers are known to contain considerable amounts of excess carbon.
Polymeric precursors to SiC have been obtained by redistribution reactions of methyl-chloro-disilane (Me.sub.6-x Cl.sub.x Si.sub.2, x=2-4) mixtures, catalyzed by tetraalkyl-phosphonium halides which U.S. Pat. No. 4,310,481, U.S. Pat. No. 4,310,482 and U.S. Pat. No. 4,472,591 teach. In a typical preparation, elemental analysis of the polymer was employed to suggest the approximate formula [Si(Me).sub.1.15 (H).sub.0.25].sub.n, with n averaging about 20. The reaction is fundamentally different than that involved in the process and the structures of the polymers are also entirely different, involving what is reported to be a complex arrangement of fused polysilane rings with methyl substitution and a polysilane backbone.
The formation of carbosilane polymers with pendent methyl groups as by-products of the “reverse-Grignard” reaction of chloromethyl-dichloro-methylsilane. The chief purpose of this work was the preparation of carbosilane rings and the polymeric byproduct was not characterized in detail nor was its use as a SiC precursor suggested. Studies of this material indicate that it has an unacceptably low ceramic yield on pyrolysis. These polymers are related to those described in the instant process and are obtained by a similar procedure, however, they contain twice the required amount carbon necessary for stoichiometric silicon carbide and their use as SiC precursors was not suggested. Moreover, the starting material, chloromethyl-dichloro-methylsilane, contains only two sites on the Si atom for chain growth and therefore cannot yield a structure which contains .tbd.SiCH.sub.2- chain units. On this basis, the structure of the polymer obtained, as well as its physical properties and pyrolysis characteristics, must be significantly different from that of the subject process.
U.S. Pat. No. 4,631,179 teaches a polymer which is a product of the ring-opening polymerization of (SiH.sub.2 CH.sub.2).sub.2 also has the nominal composition “SiH.sub.2 CH.sub.2”. However, the actual structure of this polymer is fundamentally and functionally different from that of the instant process. Instead of a highly branched structure comprised of SiR.sub.3 CH.sub.2-, —SiR.sub.2 CH.sub.2-, .dbd.SiRCH.sub.2-, and .tbd.SiCH.sub.2- units, the Smith polymer is reported to be a linear polycarbosilane which presumably has only [SiH.sub.2 CH.sub.2] as the internal chain segments. Such a fundamental structural difference would be expected to lead to quite different physical and chemical properties. The fundamental difference in these two structures has been verified by the preparation of a linear polymer analogous to polymer and the comparison of its infrared and H-NMR spectra.
Another important difference between the process of Smith and the instant process is the method used to obtain the product polymer and the nature of the starting materials. The [SiH.sub.2 CH.sub.2].sub.2 monomer used by Smith is difficult and expensive to prepare and not generally available, whereas the chlorocarbosilanes used in the instant process are readily available through commercial sources.
U.S. Pat. No. 4,923,716 teaches chemical vapor deposition of silicon carbide which uses a “single molecular species” and which provides reactive fragments containing both silicon and carbon atoms in equal number this process. Linear and cyclic structures of up to six units are mentioned. These compounds, which include both silanes and carbosilanes, are specifically chosen to be volatile for chemical vapor deposition use, and are distinctly different from the instant process, where the products are polymers of sufficiently high molecular weight that they cross-link before significant volatilization occurs. Such volatility would be highly undesirable for the applications under consideration for the polymers of the instant process, where excessive loss of the silicon-containing compound by vaporization on heating would be unacceptable.
The inventors hereby incorporate the above-referenced patents and articles into this application.